Only a shadow of the 3d object over the background is visible in the render
You are multiplying the image on top of the background.

Use alpha over to place the render layer over the background.



  Use this node to layer images on top of one another. This node takes two images as input, combines them with a factor, and outputs the image. Connect the Background image to the top input, and the foreground image to the lower input. Where the foreground image pixels have an alpha greater than 0 (namely, have some visibility), the background image will be overlaid.


Please read the manual: https://www.blender.org/manual/compositing/types/color/alpha_over.html?highlight=alpha%20over